Heat responsive marking sheets



May 25, 1965 CO-CRYSTAL ADDUCT OF AN AMINE AND A HYDROXYPHENOL COMPOUNDA PHENOL 0 NITROPHENOL AN OXIDANT SUPPORT v INVENTORS MICHAEL E BAUMANNBYWILLIAM R. LAWTON ATTORNEYS United States Patent "ice 3,185,584 1 HEATRESPONSIVE MARKING SHEETS Michael F. Baumann, Hudson, and, William R.Lawton, Nashua, N.H., assignors to Nashua Corporation, Nashua, N.H., acorporation of Delaware Filed Nov.19, 1962, Ser. No. 238,712

4 Claims. (Cl. 117-36.8)

This invention relates to thermographic copying sheets and isparticularly concerned with a copy sheet which is characterized by itsability to form a colored image of a color contrasting to thebackground; wherever the sheet is exposed to heat.

The exposure may be made through a master copy which is exposed toradiant energy. That energy is converted to sensible heat in theindi-cia appearing on the master sheet. Consequently the copy sheet issubjected to selective, localized heating under theindica and a coloredimage of the original indica appears. In recording apparatus, the sheetis heated directly by a hot stylus.

For brevity, both such modes of heating will be referred to as thethermographic process.

The present invention is a continuation of work begun in theapplications of. William R. Lawton and Eugene F. Lopez, Serial No.808,012, =filed April 22, 1959, now US. Patent No. 3,076,707, and theapplication of William R. Lawton (sole) Serial No. 206,186, filed June29,

1962, both of which are assigned to the assignee of this invention. Theentire disclosure of both above identi fied applications is hereinincorporated by reference.

The above applications disclosed that the co-crystal adducts of abisphenol and an amine, or a hydroxyphenol substituted chroman and anamine can be coated on a copy sheet wherethey remain inert andnon-reactive. When heated to between 50 and 150 C. however, thesecomplex crystals dissociate; releasing the amine which thereupon canreact with materials with which it is in intimate contact. In the twoapplications mentioned above onesuch material is an azo compound whichis developed or changed in color by the amine which has beenreleased bythe heat of the thermographic process.

We have now discovered that when the amine is heatreleased from acocrystal adduct in the presenceof an oxidizing agent and a substancewhich gives rise to a color change upon oxidation, a good, intense, andhighly responsive color change occurs. When a sheet coated with acomposition including thesevari-ous materials is used in a.thermographic copying process a satisfactory reproduction of theoriginal indica results.

The color change is not entirely due to a change in color of the oxidantwhen it is reduced, but is evidently due in great part to the ability ofthe oxidant to promote a change in colorin the substance which isoxidized.

Among the substances capable of acting as oxidants in tbis envir'onmentare compounds such as copper nitroprusside (CuFe(CN )NO), nickelnitroprusside (NiFe(CN )NO) sodium nitroprusside (Na Fe(CN )NO.),copperoxalate, potassium ferricyanide, and the eerie salts. Sodiumnitroprusside is preferred because ofits ability not only to act as anoxidizingagent (the complexed iron goes from plus three to plus two),but because it apparently also forms a complexed material with theresulting product, especially with oxidized oxygen, nitrogen or sulfolinkages. i

Compounds which are capable of being oxidized in this reaction includecompounds with the grouping HO- aromat-ic-OH, HO-aromatic-arornatic,HO-aromatic-NH The comounds having the groupings tri-OH-arOmflfiiCQ HO-a-romatic-S, and H Naromatic (s)-NH give superior performance. V x

Patented May 25, 1965 Among the oxidizable materials which give goodresults are gallic acid, phloroglucinol, P-phenylenediamine, benzidene,tannic acid, pyrogallal, hydroq-uinone, and O- phenylenediamine. Ofthese pyrogallol and its derivatives,

.benzidene and the phenylenediamines are preferred.

found to be operative. Among such carriers may be mentionedtetrachloro-bisphenol A, tetrabromobisphenol A, 2,2-thiobisnaphol, andthe hydroxyphenol substituted ohromans. As a class, the co-crystaladducts of amines bisphenols are well known. Many are described in US.Patent 2,829,175. The hyd-roxyphenol substituted chroman :co-crysta-ladducts are described by Cramer, EIN- SCHLUSSVERBINDUNGEN, (published bySpringer- Verlag, Berlin, 1954).

The useful amines include ethanolamine, diethanolamine, triethanolamine,N-methylethanolamine, phenyl ethanolamine, propyleneamine,polyglycolamine, tetramethylguanidine, and ethylenediamine. The alcoholamines are preferred.

All combinations of these carriers and the amines heatdecompose withinthe range of heats which are practicable in the thermographic process,namely 50 to 150 C. and, upon thermographic heating, provide a favorablemedium for reactivity.

Copy sheets are prepared by dispersing 10 parts of each of the activematerials in parts of a 2.5% solution of a resinous binder dissolved ina suitable solvent. When the desired particle size of each ingredienthas been reached, the dispersions are combined by simple mixing. Thedispersion mixture is then coated on a suitable supporting sheet, e.g.glassine. A coating weight of approxi mately 5 lbs. per ream of 24" x36" x 500 sheets is effective. The accompanying drawing illustratesschematically a heat sensitive sheet corresponding to this invention.The sheet is represented as being in cross section.

PREPARATION OF THE BISPHENOL/AMINE ADDUCT Example 1 The solid molecularcomplex adduct of Tetrachlorobisphenol A and Diethanolamine is preparedin the following manner. 1 mole (366 grams) of Tetrachlorobisphenol A isdissolved in 1098 grams of toluol with heat. To this solution is added 2moles (210 grams) of Diethanolamine with constant agitation. A finecrystalline precipitate is obtained and the crystals are collected byfiltering and are washed three times with norm-a1 hexane and allowed todry. The product is the ad-duct-Tetradhlorobisphenol A/Dietho-nalamine(TCBA/ DEA) In the foregoing example, the bisphenol used wastetrachlorobisphenol A (4,4'-isopropylidene-bis-(2,6-dichlorophenol). Wehave found that this material is efifective in the formation of numerousof the co-crystal adducts which dissociate at temperatures within therange of about 50+150 C., but other bisphenols are available and areuseful. These other bisphenol compounds may be employed in thepreparation of solid heat-dissociable co-crystal adducts with amines.Compounds which are preferred include tetrabromobisphenol A;4,4'-isopropylidene-bisphenol; 2,2 methylene bis(4-methyl-6-butylphenol); 4,4'-thio-bis-(6-tert. butyl-m-cresol);4,4-,butylidene-bis-(G-tert. butyl-m-cresol);2,2-thio-bis-(4,6-dichlorophenol) 2,2methyl-4,4'-bis-(3,4,6-trichlorophen01), and 2,2-thiobisnaphthol. Otherbisphenol compounds which may be used in this manner are set forth inthe previously mentioned Patent, 2,829,175.

PREPARATION OF THE CHROMAN ADDUCTS Example 2 A hydroxyphenol substitutedchroman, namely 2'-hydroxy-2,4,4,7,4-phentamethylflavan is preparedaccording to a procedure described by Baker and Besley in J. Chem. 80.,1951, 1102-6. A mixture of m-cresol (440 g.) and acetone is saturatedwith gaseous HCl without cooling and kept at 40 C. for two days with theexclusion of water. The dark product is added to an excess of 20% sodiumhydroxide solution, a layer of ether is poured on the surface, and themixture is vigorously stirred causing the ether addition product of thedimeride to crystallize. After standing overnight in an open vessel thesolid is collected, washed thoroughly with water, dissolved in hexane,and dried with calcium chloride. The solution is filtered and a smallamount of 'ether is added to the solution. The ether complex of theflaven compound separates in large, colorless, thick 'rhombic prismshaving a melting point of 7677 C. A fiaven co-crystal adduct is preparedby mixing fifteen parts of a 10% hexane solution of the flavan ethercomplex with 7.5 parts of dicyclohexylamine, chilling the mixtureovernight, and filtering the solid crystalline adduct product, M.P.103-105 C.

While the above flavan material is one which we have found to beeffective in the formation of numerous cocrystal adducts which exhibitdissociation temperatures within the range of about 50-l50 C. it is notthe only available or useful hydroxyphenol substituted chroman. Numerousother hydroxyphenol substituted chromans may be used and among thesewhich we prefer are 7,4'-diethyl-2'-hydroxy-2,4,4-trimethyl flavan;cyclohexanespiro-4-(2'-hydroxy-7,4-dimethyl 2,3 tetramethylene) flavan;2' hydroxy 2,4,4,6,7,4,5 heptarnethyl flavan;2-hydroxy-2,4,6,5'-pentamethyl flavan; 4-p-hydroxyphenol-2,2,4trimethylchroman. As in the case of the bisphenols, many amines are suitable, themost effective being the alcohol amines. The chroman adducts cannormally be prepared by simple mixing of the selected chroman and aminein the manner shown above.

7 These adducts are incorporated in a coating composition as follows:

Example 3 (A) Ten parts of sodium nitroprusside is added to 90 parts ofa 2 /z% solution of polyvinyl butyral (Butvar B-76) in trichloroethyleneand ground in a ball mill until the nitroprusside is reduced to fineparticle size.

(B) Ten parts of pyrogallol is added to 90 parts of a 2 /2 solution ofpolyvinyl butyral in trichloroethylene and ground in the same manner.

(C) Similarly, 10 parts of the co-crystalline adduct oftetrachlorobisphenol-A and diethanolamine is added to 90 parts of a 2'/2% solution of polyvinyl butyral in trichloroethylene and ball milledas above.

When the desired particle size is reached, the three dispersions arecombined in the ratios of solid ingredients as follows:

Parts (A) Sodium nitroprusside 2 (B) Pyrogallol 2 (C)TCBA/diethanolamine 4 After thorough stirring, the combined dispersionsthen form the coating composition which is spread by conventionalcoating machinery on a suitable supporting sheet, e.g. thin paper havinga ream weight of 22 lbs. per ream of 500 sheets, 24" x 26". The dryWeight of the coating is approximately 5 lbs. per ream. After thevolatile suspending medium has evaporated, the sheet will produce a deeppurple image when exposed in thermographic apparatus.

4 The following coating compositions all prepared as set forth inExample 3 were combined in the ratios of solid ingredients as follows.

(Imageblack-brown.)

The hydroxyphenol substituted chroman adducts may be substituted for thebisphenol adducts of the preceding examples with substantially the sameresult, but because of their water insensitivity it is convenient, attimes, to apply a first coat containing only the chroman adductsuspended in a water solution of a water-soluble binder, e.g. polyvinylalcohol, carboxymethyl cellulose, hydroxyethyl cellulose, or gums. Insuch cases, the aqueous first coat which is applied to the supportingsheet at the dry weight of approximately 4 lbs. per ream of 24" x 26" x500 sheets may be as follows.

Example 8 Parts 2-hydroxy-2,4,4,7,4-pentamethyl flavan/ethylenediamine'20 Polyvinyl alcohol 2 Water 98 When the coating is dry it isovercoated to a dry weight of about 2 lbs. per ream of the followingcoating composition.

Ratios of solid ingredients:

Parts Sodium nitroprusside (dispersed in trichloroethylene as in Ex. 3)4 Pyrogallol (dispersed in trichloroethylene as in Ex. 3) 4 When thesecond coat is dry, this sheet, when exposed to heat in thermographicapparatus, will produce a deep purple image.

Sodium aminopentacyanoferroate (Na Fe(CN) -NH and Gallic acid underthese conditions will produce a purple image on a yellow background.When phloroglucinol is the oxidizable substance, the image is black.Ceric sulfate, or ceric ammonium sulfate with gallic acid will produce adeep brown image. Copper Oxalate and p-phenylenediamine or benzidineform coatings having excellent heat response and produce strong, greenimages. The combination of sodium nitroprusside and 1,5-naphthalenediolproduces a brown-black image. With 1,1- thiobisnaphthol, the image isviolet; with benzidene, black. Copper nitroprusside and nickelnitroprusside give results similar to those of the sodium salt, butcopper produces brown colors. With nickel, the colors are blacker.

As the paragraph above indicates many permutations of the reactants arepracticable and are, within the scope of this invention.

The process permits the manufacturer to have a substantial degree offlexibility. It permits copy sheets to be furnished which producedistinctively colored images-- often a great convenience when thesourceof copied correspondence must be quickly identified.

What is claimed as the present invention is:

1. A heat-responsive copy sheet adapted to change visibly to acontrasting color wherever subjected to localized heating to atemperature between 50 and 150 C. comprising, in combination (a) asupporting sheet carrying on a surface thereof a coating comprising -auniformly distributed intimate association of finely divided particlesof (b) an oxidizable compound selected from the class consisting ofphenols and nitrophenols,

(c) an oxidant selected from the class consisting of the nitroprussidesof copper, nickel and sodium, copper oxalate, potassium ferricyanide,ceric sulfate, and ceric ammonium sulfate, and

(d) a solid, normally stable, co-crystal adduct comprising the reactionproduct of an amine and an hydroxyphenol compound selected from theclass consisting of bisphenols and hydroxyphenol substituted chromans,and which is heat dissociable in the temperature range of 50 C. to 150C.

2.. A heat-responsive copy sheet as claimed in claim 1 wherein theoxidant is sodium nitroprusside, the oxidizable compound is pyrogallol,and the co-crystal adduct is the adduct formed by tetrachlorobisphenol-Aand di- ,ethanolarnine.

3. A heat-responsive copy sheet as claimed in claim 1 wherein thecoating comprises a first layer comprising an hydroxy phenol substitutedchroman adhered to the supporting sheet by a water-soluble binder, and asecond layer co-extensive with said first layer comprising the oxidantand the oxidizable compound adhered to said first layer by a resinousbinder.

4. A heat-responsive copy sheet as claimed in claim 1 wherein theco-crystal adduct is 2'-hydroxy-2,4,4,7,4'-

pentamethyl fiaven/ethy-lenediamine, the oxidant is sodiumnitroprusside, and the oxidizable compound is pyrogallol.

References Cited by the Examiner UNITED STATES PATENTS 2,813,042 11/57Gordon et a1. 4736.8 2,995,466 8/61 Sorensen 47-368 3,024,362 3/62 Su-set al 4736.8 3,031,329 4/62 Winger-t 47--36.8 3,076,707 2/63 Lawton eta1. 4736.8

WILLIAM D. MARTIN, Primary Examiner.

RICHARD D. NEVIUS, MURRAY KATZ, Examiners.

1. A HEAT-RESPONSIVE COPY SHEET ADAPTED TO CHANGE VISIBILY TO ACONTRASTING COLOR WHEREVER SUBJECTED TO LOCALIZED HEATING TO ATEMPERATURE BETWEEN 50* AND 150*C., COMPRISING, IN COMBINATION (A) ASUPPORTING SHEET CARRYING ON A SURFACE THEREOF A COATING COMPRISING AUNIFORMLY DISTRUBTED INITMATE ASSOCIATION OF FINELY DIVIDED PARTICLES OF(B) AN OXIDIZABLE COMPOUND SELECTED FROM THE CLASS CONSISTING OF PHENOLSAND NITROPHENOLS, (C) AN OXIDANT SELECTED FROM THE CLASS CONSISTING OFTHE NITROPRUSSIDES OF COPPER, NICKEL AND SODIUM, COPPER OXALATE,POTASSIUM FERRICYANIDE, CERIC SULFATE, AND CERIC AMMONIUM SULFATE, AND(D) A SOLID, NORMALLY STABLE, CO-CRYSTAL ADDUCT COMPRISING THE REACTIONPRODUCT OF AN AMINE AND AN HYDROXYPHENOL COMPOUND SELECTED FROM THECLASS